This invention relates to an emitter or receiver cylinder for hydraulic brake or clutch control in a motor vehicle, of the type including an intermediate element.
More particularly, the invention relates to hydraulic control apparatus of the type comprising at least one control cylinder, wherein the cylinder includes a substantially tubular cylinder body, having an internal bore in which there slides axially a piston having a front face which delimits a hydraulic chamber, wherein a port for connection of a duct is open into the hydraulic chamber, wherein the cylinder body is stepped and comprises a front portion which delimits the hydraulic chamber and in which there is formed at least one front portion of the internal bore in which the piston slides, and a rear portion of enlarged diameter, the two portions being delimited by an annular transverse wall of the cylinder body, against which there bears axially an intermediate element received in the rear portion for axially positioning at least one internal sealing member which cooperates with the lateral wall of the piston, and wherein the said intermediate element is held axially in the rear portion by means of an annular cylindrical rear sleeve mounted in the rear portion and fixed sealingly in the latter by adhesive bonding or welding, especially by ultrasonic welding.
A control apparatus of this type is known from the document FR-A-2 741 919, in which sealing between the piston and cylinder body, for the purpose of preventing any leakage of pressurised fluid out of the hydraulic chamber, is achieved by means of a composite internal seal at the front, which is positioned axially by means of an intermediate element in the form of a ring, and which is received in an internal seal seating formed in the inner wall of the cylinder body, the sealing effect being completed by an internal seal of a lipped type at the rear, which is received in an internal seal seating formed in the inner wall of the sleeve.
Such a design makes it necessary to form seal seatings in different components. Assembly and fitting of the components and seals is not easy, and gives rise to risks of damaging the seals.
Finally, during an ultrasonic welding operation, there is again a danger of damage to the seals. It is therefore desirable to find a solution which is suitable for this method of welding as well as to other possible welding methods or adhesive bonding.
An object of the invention is therefore to propose means for sealing the hydraulic chamber which are simple, reliable, and easy to assemble, which do not oppose sliding movement of the piston by excessive friction effects, and which also offer the possibility for modular design of the apparatus with a view to standardising some components regardless of the number of internal sealing members and of the type of seal.
With this in view, the invention proposes an apparatus of the type described above, characterised in that the intermediate element is a tubular element constituting a seal carrier, having a peripheral internal wall in which at least one internal seal seating is formed which is open radially inwards towards the side wall of the piston.
Thanks to the invention, the seal is not sensitive to vibrations during the operation of ultrasonically welding the skirt and body together, and the seal is not in danger of damage. In addition, it is possible to form a sub-assembly consisting of the seal and tubular element, which is inserted into the cylinder body and which is then immobilised by fitting the rear sleeve in the cylinder body. The intermediate element permits more widespread standardisation of the control cylinder due to the fact that it forms a sub-assembly with at least one sealing member. This element may thus consist of an adapter member, in particular as a function of the construction of the sealing member or members, its dimensions, and particularly its axial length, depending on the application. In other versions, this member is standardised. Because of this intermediate element, it is possible to assemble the sleeve with the body by adhesive bonding, or by any type of welding compatible with the construction of the body and sleeve in plastics material.
In accordance with further features of the invention:
the internal seal seating is open axially forward, and the seal which it receives is retained axially towards the front by the said annular transverse wall of the cylinder body, against which the intermediate seal carrier element bears axially, so that the body is simplified;
the internal seal seating is open axially towards the rear, and the seal which it receives is retained axially towards the rear by an annular front transverse end face of the sleeve, which is thereby simplified;
the intermediate seal carrier element carries two internal dynamic sealing members, namely a front seal and a rear seal, which are received in an internal front seating and rear seating, respectively, which are open axially towards the front and the rear respectively;
the internal sealing member received in the said internal seating which is open axially forward is a composite seal which comprises an inner ring of material having a low coefficient of friction, which is clamped radially against the side wall of the piston by an annular external ring of elastomeric material which is received in the said internal seating;
the internal sealing member which is received in the said internal seating open axially towards the rear is a lipped sealing cup member for radial frictional engagement;
includes an external sealing member which is interposed operatively between the outer periphery of the intermediate seal carrier element and the inner periphery of the rear portion of the cylinder body, in order to protect the zone in which the body and sleeve are assembled together;
the external seal is received in an external seal seating formed in the intermediate seal carrying element and open radially outwardly towards the inner periphery of the rear portion of the cylinder body;
the said external seal seating is open axially towards the front, and the external seal which it receives is retained axially towards the front by the said annular transverse wall of the cylinder body against which the intermediate seal carrying element bears axially;
the intermediate seal carrier element is held clamped axially between the said annular transverse wall of the cylinder body and the transverse annular front end face of the sleeve;
the cylinder body and the sleeve are made of plastics material;
the intermediate seal carrier element is made of plastics material;
the free rear end portion of the sleeve projects axially beyond the rear axial end of the cylinder body and carries abutment means for limiting the axial rearward travel of the piston with respect to the cylinder body;
the said abutment means consist of a ring including a cylindrical axial skirt which surrounds the axial rear end portion of the sleeve, with respect to which it is retained axially, the said ring that includes a transverse base having a through hole for passage of the rod of the piston, and constituting an annular transverse abutment with which the axial rear end of the piston is arranged to cooperate;
the axial skirt of the end stop ring is telescoped elastically over the axial rear end portion of the sleeve;
the transverse abutment base of the abutment ring is offset axially towards the rear with respect to the transverse axial rear end face of the sleeve;
the apparatus includes a bellows for protection and sealing, mounted on the cylinder body and on the piston rod;
the bellows includes a cylindrical axial front skirt for fastening it on the rear axial end portion of the sleeve which surrounds the skirt of the protective ring;
the piston extends through the intermediate seal carrier element with a radial clearance;
the sealed welding zone between the sleeve and the rear portion of the cylinder body is offset axially towards the rear with respect to the intermediate seal carrier element;
the sleeve is a sleeve for guiding the piston in sliding movement, and for this purpose, its internal cylindrical wall constitutes a rear portion of the internal bore of the cylinder in which the piston is mounted sealingly for sliding movement.